In the United States, SMS spam annoys users and elevates phone bills. Users can download antispam software or block SMS with the carrier, but in the end, it's the victim who pays.

My father's Motorola E815 from Verizon is suffering chronic SMS, or text message, spam. At first, the unwanted messages trickled in--religious messages with pictures of saints one time, pharmaceutical marketing another. Then the spam rate escalated. After one spammy text message yesterday and two this morning, Dad decided he wanted out.

"Out" in his case, and in the case of most North American mobile phone users, is as much about the phone bill as it is receiving unwanted texts. Service providers like Verizon and T-Mobile charge for inbound and outbound SMS activity, either per message, generally 10 cents to 15 cents per outgoing text message, or as part of a larger service, usually between $5 and $10 more per month depending on the plan. Data downloads cost extra too, so spam texts with image attachments ratchet up the bill. "This was becoming an expensive habit," says Dad.

The kicker, of course, is that it's not his habit.

So what does it take to stop unwanted SMS spam? The weed-whacking process is a lot thornier than it would seem. One option is to block messages through the carrier, but allowances vary. Verizon, for example, permits customers to flatline all e-mail and Web messages, and add up to 15 known offenders to a blacklist. It does not, however, let customers protect known senders in a white list.

Investing in security software with an antispam component is another option. Major players like Symantec, TrendMicro, and BitDefender have developed mobile versions of their signature software, and F-Secure has stepped further by striking a deal with Nokia to pre-install F-Secure Mobile Anti-Virus on select Nokia models.

Purchasing $50 worth of security to stymie SMS spam seems like overkill for most North and South American users who haven't yet seen the mobile exploits that Asian and European users have. Of course, mobile attacks are growing worldwide, but it's hard to imagine users adopting mobile security en masse until the problems become both widespread and unavoidable.

So why don't the carriers do us users a favor and squash the spam? Is it a question of instituting the filters and qualifying senders, or is it simply more profitable to do nothing? For each inbound SMS a pay-per-text customer receives, another few cents clatter into the carrier's piggy bank. Those pennies add up quickly among several million users.

I'd be ready to jump on the greedy-service-provider train, except that a laissez faire attitude threatens to alienate, or at least substantially irritate, customers who subscribe to plans with unlimited text messages. It may be that customers will continue to shake the short end of the stick at unresponsive service providers until text spam grows too frequent to ignore. (I'm imagining a spontaneous uprising where angry users repeatedly text carriers their demands to end the spam madness.)

In the meantime, users face Viagra and bogus stock-tip ads alone, possibly at the expense of their availability via text, or at the expense of their wallet. The message rings loud and clear--in mobile spam, it's the customer who ultimately pays.

Jessica Dolcourt reviews smartphones and cell phones, covers handset news, and pens the monthly column Smartphones Unlocked. A senior editor, she started at CNET in 2006 and spent four years reviewing mobile and desktop software before taking on devices.